Diesel, gasoline, and alcohol fueled internal combustion engines find broad application in both motor vehicles and stationary applications like motor-generators.
Many such engines use hydrocarbon-based, oil lubricating systems in which the oil is pumped during engine operation from an underlying reservoir, up and over the pistons, cylinder walls, inlet and exhaust valves, cranking mechanisms and other parts of the operating engine, and drained back through the crankcase and into the oil pan or sump. The circulating oil is pumped through an oil filter for removal of solids that are introduced into the oil by the combustion process or wear of engine parts. But water, and unburned or partially burned fuel constituents such as low molecular weight hydrocarbons, and/or alcohol are also introduced into the circulating oil. These liquid and vaporous materials are not removed by the oil filter and may reduce the useful life of the oil and have potential for causing corrosion of engine surfaces.
Such engines may also have a Positive Crankcase Ventilation (PCV) system which uses the engine air induction system to circulate air through the crankcase above the oil reservoir, to clear gases and vapors out of the crankcase and from the oil. These crankcase gases and vapors are inducted into the PCV airflow and carried, first, into the engine air inlet manifold, and then into the engine cylinders, where they may be consumed and exhausted from the engine.
Thus, in engine operation, some portion of the products of combustion and unburned fuel (water, alcohol, small hydrocarbons) mix with the circulated engine oil. When the engine has been operating long enough for the circulating oil to reach a temperature of, for example, about 100° C., these contaminants are vaporized and continually removed from the oil and crankcase. But, during short term vehicle usages, the engine does not run long enough to heat the oil to temperatures high enough to expel such contaminants into the PCV system. The water, or alcohol, or fuel species remain in the oil where they may corrode engine parts.
Such low engine oil temperatures are commonly encountered on first starting an engine which has not been run for some period, but, of course, under most engine operating modes, this low engine oil temperature condition is temporary. With continued engine operation, the oil temperature will rise; the contaminants will substantially vaporize, accumulate in the crankcase, and be swept away by the PCV system.
However, in some circumstances and applications, an engine may be operated sporadically and for only short periods of time, resulting in a persistently low oil temperature. This condition may be encountered, for example, in a vehicle repeatedly used for infrequent short trips, or, in a hybrid-electric vehicle, where the auxiliary engine used to charge the battery is used only occasionally.
Under these conditions, the condensed contaminants may be retained in the engine oil for some appreciable period of time and contribute to premature oil degradation. There is therefore a need for improved methods of managing the concentrations of water, alcohols and low molecular weight hydrocarbons in oil, particularly at low engine oil temperatures.